This invention relates to a process for the production of film-forming chlorinated polymers which, as lacquer films, are highly resistant to water.
1. Field of the Invention
Aliphatic polymers, such as natural rubber, polyisoprene, polybutadiene, polyethylene, polypropylene and polyethylene-propylene copolymers, may be chlorinated by introducing gaseous chlorine into a solution of the polymer in a chlorine-resistant organic solvent, for example at from 60.degree. to 120.degree. C. The chlorine-resistant solvent normally used is carbon tetrachloride which, although particularly suitable, necessitates specialised safety measures for ecological reasons. On completion of the chlorination reaction, the polymer may be recovered in solid form from solution in the chlorine-resistant organic solvent by treating the mixture with hot water or steam. Some of the organic solvent used distills off, while the chlorinated polymer precipitates and may be filtered off. The main product obtained then contains from 30 to 60%, by weight, of water in addition to considerable residues of the organic solvent. The organic solvent is not completely removed even by drying the product in vacuo or in a gas stream. For example, from 5 to 10 parts, by weight, of organic solvent remain 100 parts, by weight, of the chlorinated polymer (cf. German Offenlegungsschrift No. 2,359,461=U.S. Pat. No. 4,144,203).
For use as a coating composition, the chlorinated polymer is dissolved in a conventional lacquer solvent, for example, toluene. The remaining residues of the chlorination solvent, mainly chlorinated hydrocarbons, pass into the solution and evaporate on coating. To avoid this, the residue of chlorination solvent in the chlorinated polymers used for coating purposes has to be reduced.
2. Description of the Prior Art
It is known (cf. German Offenlegungsschrift No. 2,701,288=U.S. Pat. No. 4,122,249) that, when the solution of the chlorinated polymer in the chlorine-resistant organic solvent is treated with hot water or steam, it is possible to add to the solution a small quantity, by weight, of an aliphatic alcohol containing at least 8 and preferably 12 carbon atoms in order to reduce the residue of chlorination solvent in the chlorinated polymer. However, this process is attended by the disadvantage that the precipitated product tends to stick to the walls of the precipitation vessel. In addition, a further reduction in the residual solvent content appears desirable (cf. also German Offenlengungsschrift No. 2,559,461).
Improved results are obtained (cf. German Offenlegungsschrift No. 2,818,647=U.S. Pat. No. 4,172,104) when the treatment of the solution of the chlorinated polymer in the chlorine-resistant organic solvent with hot water or steam is carried out in the presence of a small quantity, by weight, of an ethoxylation product of 1 mole of a primary aliphatic mono-hydric alcohol containing at least 8 carbon atoms and from 2 to 20 moles of ethylene oxide.
From 70 to 80% of the ethoxylation product remains in the chlorinated polymer.
A major disadvantage here is that, as lacquered films, the chlorinated polymers precipitated using ethoxylated aliphatic alcohols have a lower resistance to water than corresponding films of additive-free chlorinated polymers.